The invention relates to a method of preparing a system of converting tools in a stripping station in a converting press, the converting-tool system comprising at least one central stripping board and an upper stripping die with a stripper-holder plate.
The invention also relates to a presetting table for working the method. The invention also relates to an assembly of components comprising a stripper-holder plate and a set of strippers for preparing an upper stripping die.
Presses for converting compact cardboard or corrugated cardboard sheets for production of packagings usually comprise a number of sucessive stations in the press, through which the sheets travel in succession. Starting from an infeed device or feeder, the sheets travel at a timed rate through a diecutting station where each sheet is cut into one or more blanks which remain interconnected by connections and entrain waste pieces of sheet situated around and between them, a stripping station where the cutting waste is removed, and a blank separating station where the connections are broken, after which the blanks are stacked.
In the stripping station the cut sheet is placed on to a wooden board with apertures, i.e. the central stripping board, formed with a plurality of pre-cut apertures. The apertures are disposed opposite the waste pieces of sheet and have an overall shape corresponding thereto, with a somewhat larger outline. The stripping operation is performed by using at least one movable upper stripping tool which descends perpendicularly to the cardboard sheet and pushes the waste through the apertures in the central stripping board.
The upper stripping tool is frequently an upper stripping die comprising a wooden board on to which strippers are fixed by screwing, nailing or sticking at places corresponding to the waste to be stripped, the strippers having varying forms adapted to the shape of the waste, such as nails, pins, strips or blocks of wood. Preparation of such a stripping die requires lengthy, meticulous work by a die-maker, and a stripping die can be used for only a single cutting pattern. If the manufacturer needs to perform a large number of different recurring jobs, in small or medium series, a corresponding number of different stripping dies, each costing several hundred Swiss francs to make will have to be constructed and stored.
To obviate this disadvantage, Swiss patent application CH 1417/99 by the Applicant describes a universal stripping tool comprising a stripper-holder plate comprising a pair of identical metal sheets formed with a large number of perforations over their entire surface and mounted on a tubular frame. The strippers are chosen from among rectangular blocks comprising magnetic fixing studs and stripping pins in the form of a rod bent twice at right angles to form a U having two arms of unequal length inserted simultaneously into two pairs of perforations in the two perforated metal sheets and remaining held there by the relative elasticity of the two arms.
Patent CH-682651 describes a movable upper tool in a blank separating station, comprising punches carried by a board formed with openings through which air flows. The lower surface of the board is covered with a layer of xe2x80x9cvelcroxe2x80x9d or similar hook-fibers. The upper surface of each separating punch is covered with a second layer of xe2x80x9cvelcroxe2x80x9d or similar mating hook fibers adapted to engage the layer of fibers covering the board and securing the punch to the board. The punches are arranged in a manner corresponding to the positions of the connections between the blanks in a sheet. This tool is modified for each job and avoids the need to store a large number of blank separating tools, each corresponding to a given job.
Automatic converting presses are capable of processing several thousand sheets per hour. Short series of blanks for packagings themselves comprise only a few thousand articles. It is therefore essential for economic reasons to be able to change from one job to another, i.e. to prepare the converting tools and insert the tools in the machine, adjust them to size and secure them, without stopping the machine for more than a few minutes.
The actual operation for fixing the strippers and punches mentioned hereinbefore to their supports is brief but very tricky, since an error in positioning may result in jamming the machine. Preparation therefore requires laborious corrections.
One aim of the invention is to propose means for rapidly preparing the converting tools, more particularly the converting tools in the stripping station, during masked time, i.e. while the machine is carrying out a different job, by drawing from a limited stock of standardised components. Another object of the invention is to prepare the tools in such a way that they can be positioned in the station without requiring laborious adjustments. Finally, preparation should be as accurate as the work of a die-maker.
The invention therefore proposes a method of preparing a system of converting tools in a stripping station of a converting press comprising at least one central stripping board and an upper stripping die with a stripper-holder plate, comprising the following steps:
the central stripping board and the stripper-holder plate are disposed face to face outside the converting press and fixed in an adjustment position,
the strippers are fixed to the stripper-holder plate in line with the apertures in the central stripping board in order to form the upper stripping die,
the upper stripping die and the central stripping board are placed and centered in the stripping station.
The method can be worked according to the invention by means of a presetting table comprising a frame, bearing support means and means for fixing the stripper-holder plate, means for supporting the central stripping board in order to hold a central stripping board in contact with or near a stripper-holder plate, and means for fixing the central stripping board, chosen so as to fix a central stripping board in the adjustment position.
In the method according to the invention, the central stripping board serves as a template for rapidly and accurately positioning the strippers on the stripper-holder plate.
The presetting table according to the invention can be used to effect this operation in reliable manner without worrying about the respective positions of the stripping board and the stripper-holder plate once fixed to the table, since the table holds them in the correct adjustment position without risk of accidental displacement while the operator is fixing the strippers on the plate.
The user in principle need store only two stripper-holder plates, one in operation in the machine at work whereas the other is prepared outside the machine for the next job. A small number of plates is sufficient in every case.
Preferably, the strippers and the stripper-holder plate are designed so that the strippers can be placed and fixed to the plate manually and removably, so that their arrangement can be altered when required.
Preferably, in the adjustment position, the stripper-holder plate and the central stripping board are in the same relative positions, seen in projection on to a plane parallel to the central stripping board, as the positions which they occupy when placed in the stripping station, when they are centered laterally with respect to the machine axis and adjusted longitudinally to the first rule. If this adjustment position in the presetting table is adopted, there will be no need for an additional adjustment operation when the tools are inserted into the stripping station.
Terms such as xe2x80x9clongitudinalxe2x80x9d, xe2x80x9clateralxe2x80x9d, xe2x80x9cfrontxe2x80x9d and xe2x80x9crearxe2x80x9d are used here with reference to the direction of advance of the sheets in the machine. The machine axis is a virtual axis in the direction of advance, used as a reference for all adjustments of components of the converting press in the transverse direction.
The term xe2x80x9cfirst rulexe2x80x9d refers to the first transverse rule of the shape for cutting in the diecutting station.
In present-day converting presses, the converting tools usually comprise reference and locking means such as stops and studs, corresponding to mating reference and locking means on the machine, so that the tools can be quickly and reproducibly centered when positioned, laterally with respect to the xe2x80x9cmachine axisxe2x80x9d and longitudinally with respect to the longitudinal stop positions of the sheet-driving system and to the longitudinal positions of the other tools with which they co-operate, particularly the first rule. In working the invention, the position of a stripping die and/or a stripping board outside the machine can be determined via the front edge of the plate or board respectively and by means of a centering stop co-operating respectively in the machine with a support surface and a slot or notch in a stud on a stand or frame of the station where the tool is used.
In order to place the stripper-holder plate and the central stripping board in the adjustment position mentioned hereinbefore, the presetting table comprises two parallel support bars for the front edges of the stripper-holder plate and of the central stripping board, offset from one another if required so as to reproduce the longitudinal adjustment of the machine to the first rule. The presetting table can comprise two fixed adjustement studs each having a notch, slot or slideway adapted to receive the stops for centering on the respective machine axis of the central stripping board and of the stripper-holder plate, the two notches/slots/slideways being centered relative to the same plane perpendicular to the plane of the central stripping board and perpendicular to the support plane of a support bar.
Preferably, the support bars of the presetting table are contiguous, so that the stripper-holder plate and the central stripping board are in contact with one another in the adjustment position. This makes it easier to position the strippers accurately.
In order to hold the stripper-holder plate in position in the presetting table, the table can comprise a latch, disposed on its stand so as to come into engagement with the rear edge of the stripper-holder plate. To allow for different possible dimensions of the stripper-holder plate, the latch can be mounted on a movable carriage sliding on the stand in the direction of the table which corresponds to the machine axis.
In order to hold the central stripping board against the stripper-holder plate, the presetting table may also comprise an arm pivoting in a plane parallel to the plane of the board and having a pivot axis disposed above the support bar and at a distance therefrom greater than the maximum longitudinal size of the board and the plate. At its free end, the support arm can carry a presser finger provided with a spring return system exerting a pressure which holds the stripping board against the stripper-holder plate.
The system of converting tools in a stripping station can also comprise a lower stripping gripper tool comprising a plurality of gripper tools such as telescopic pins and one or more gripper tool-holders. Gripper tool-holders of this kind comprise e.g. adjustable bars disposed and fixed in a pull-out frame in the stripping station, carrying means for fixing in longitudinally and laterally pre-indexed positions.
Advantageously, the method according to the invention includes a step of adjusting the lower stripping tool wherein the gripper tool-holder or holders are brought into an adjustment position in line with the central stripping board which itself is fixed in the adjustment position facing the upper stripping die formed. This adjustment position of the gripper tool-holder or holders, seen in projection on to a plane parallel to the stripping board, is the same as the position occupied in the stripping station relative to the central stripping board. When the gripper tools are telescopic pins, they are positioned so that the free points of the pins are adjusted in contact with the strippers.
Preferably, the support for the gripper tool-holder or holders of the presetting tables is movable and adapted to be moved between the position for adjusting the gripper tools and a moved-aside position giving an operator access to the central stripping board in order more easily to position or adjust the positions of the various tool-holders and tools.
When the converting press is equipped for receiving the telescopic pins carried by the adjustable bars, which in turn are carried by a pull-out frame of the stripping station comprising a plurality of bar-fixing means in an indexed arrangement, the presetting table comprises a frame pivoting on a pivot axis situated on the stand of the presetting table and comprising the same plurality of bar-fixing means in the same indexed arrangement, so that the geometrical characteristics of the pull-out frame of the stripping station are reproduced in the presetting table.